The field of this invention relates to the application of spray materials to horticultural plants. The invention has utility for all known plants, inclusive of vegetable row crops, berry bushes, standard-sized fruit trees, ornamental shrubbery, grasses, and others. However, it is most useful for plants adapted to hedgerow growth, such as dwarf and semidwarf fruit trees. The apparatus of the invention can be used in conjunction with all materials which normally exist as, or which can be converted to, a sprayable form.
In a conventional crop-spraying operation, several spray materials are mixed together at a loading station in a quantity of up to several hundred gallons. The mixture is then carried to the field in the tank of a mobile sprayer unit and applied to the crops by means of a handgun or a spray boom. These devices operate on the basis of either a high-pressure stream of the liquid spray material, or a high-velocity air stream which carries injected spray material to the target foliage.
Disadvantages of these mixing and spraying procedures are numerous. Many spray chemicals are highly toxic to humans and handling of them presents a serious health hazard. Extra precautionary measures during the loading and mixing of the spray materials and during the cleaning of the tank are necessary in order to prevent skin contact, inhalation, and inadvertent swallowing of the toxic compounds. Other mixing precautions must be taken in order to obtain maximum effectiveness. Certain combinations of chemicals are incompatible; some chemicals in aqueous admixture interact over a period of time; some formulations can cause phytotoxicity to sensitive plants at different stages of growth; and excessive amounts of certain chemicals or the use of wrong ones can result in a residue problem. Moreover, once the chemicals are mixed, the operator is inflexible to supply particular trees or rows of plants with their individual chemical needs. Flushing and cleaning of the apparatus is time-consuming and dangerous, and failure to do so may result in clogging and corrosion of the tank, nozzles, hoses, pump, and other pieces of equipment. Disposal of unused spray materials in the tank presents still another problem. For lack of a better way, the material is often dumped onto the ground. This creates an environmental problem by contaminating the surrounding soil and possibly the water supply.
Conventional sprayers lack the ability to evenly apply the spray material to all foliage surfaces. Tests performed by Harrell et al. (U.S. Dep. Agric. ARS-S-65, August 1975) indicate that the bulk of the spray material never strikes its target but becomes airborne and drifts away. Wind accentuates the spray drift problem and frequently precludes effective spraying. Much of what does strike the foliage is unevenly distributed and runs off into the soil. Distribution uniformity can be improved by decreasing the droplet size. Unfortunately, smaller droplets are more susceptible to drifting. Spray drift and run-off result in waste of expensive chemicals and create both an environmental problem and a health hazard for the operator. Harrell et al. (supra) attempted to reduce spray losses by situating a collector opposite the plant from the spray nozzle and recycling the collected spray material to the nozzle. Use of the apparatus under test conditions only slightly increased the amount of spray deposited on the plant and still left 90% of the material unaccounted for.
Coverage uniformity with a conventional sprayer is complicated by other factors. The quantity of spray emitted from the nozzle per unit time is a function of pressure which is dependent upon variable factors such as nozzle wear, screen resistance, and line resistance. Moreover, spray coverage for a given nozzle output is directly related to vehicle speed. For example, when the vehicle travels uphill at a relatively slow rate, the degree of foliage coverage is significantly greater than at the faster downhill rate. This frequently results in detrimental overdosing or underdosing of the crops being sprayed.